Dihydropyrenes and photochromic compositions based thereon



United States Patent O 3,390,192 DIHYDROPYRENES AND PHOTOCI-IROMICCOMPOSITIONS BASED THEREON Luther A. R. Hall, Woodclilf Lake, N.J., andJohn A.

Gurney, Tarrytown, N.Y., assignors to Geig'y Chemical Corporation,Greenburgh, N.Y., a corporation of Delaware No Drawing. Filed Oct. 20,1965, Ser. No. 499,037 Claims. (Cl. 260-666) ABSTRACT OF THE DISCLOSURE15,16-methylene-l5,16-dihydropyrenes and polyalkyl-15,16-dimethyl-l5,16-dihydropyrenes having photochromic properties areprepared via multistep ring closure of bisphenolic compounds to yieldmetacyclophanes which 'are then subjected to several steps of oxidation,reduction and dehydrogenation. Typical embodiments are 15,16 methylenel,3,6,8 tetramethyl 15,16 dihydropyrene and1,3,6,8,15,16-hexamethyl-15,16-dihydropyrene.

Detailed description This invention relates to organic compoundsreversibly convertible from colored to colorless isomeric forms. Moreparticularly, it relates to 15,16-dihydropyrenes, which arephotochromic, that is, when exposed to light the compounds becomecolored or colorless, depending on their structure, and, when put in thedark, they revert to their original state. These valuable compounds findapplication as self-attenuating light valves in articles such as tintedsafety glass and headlights for automobiles; infrared screens, solariumwindows, display windows and automatic curtains; in informationretrieval apparatus such as computer memory core devices; toys;photocopying devices, light meters, and the like.

The compounds contemplated by the instant invention are those of theformulae:

wherein:

R and R are hydrogen, alkyl, cycloalkyl, aryl or CH Z, with the provisothat R; includes hydrogen only if R is other than hydrogen;

R is alkyl, aryl or CH Z;

R is (CH n being from 1 to 18, CR=CR or o-arylene; and

Z is chloro, bromo, cyano, carboxamido, carboxyl, or

carboalkoxyl.

ice

By the term alkyl and derivations thereof such as alkoxy are meantbranched or straight chained saturated hydrocarbon groups of from one toabout thirty carbon atoms. Representative of such groups are thusmethyl, ethyl, propyl, isopropyl, butyl, s-butyl, t-butyl, pentyl,hexyl, octyl, decyl dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl,decosyl,- tetracosyl, hexacosyl, octacosyl, triacontyl and the like.When the term alkyl is qualified by the designation lower, there isincluded branched or straight chain hydrocarbon groups of from one toabout six carbon atoms.

In certain formulae, the substituents in the 15,16-positions areattached through dashed and solid lines. This conventionally indicatesposition isomers, dashed lines being downwardly directed, solid linesbeing upwardly directed to show clearly the trans forms.

Special mention is made of an important embodiment of the instantinvention. This comprises compounds of the formula:

wherein R is as hereinabove defined.

Among the valuable members represented by this formula is mentionedl,3,6,8,l5,16-hexamethyl-l5,l6-dihydropyrene (R is CH which isphotochromic per se, and which serves as a valuable intermediate forphotochromes with a variety of functional groups.

Still another embodiment of this invention is represented by theformula:

wherein R and R are 'as above defined. Illustrative of a particularlyimportant species of this embodiment is 15,16 methylene l,3,6,8tetramethyl 15,16 dihydropyrene (R is CH and R is CH which is a valuablephotochrome per se, and which serves as an intermediate to preparecompounds of the above formulae bearing a wide variety of substituents.

Still a further embodiment of this invention is a photochromiccomposition comprising a dihydropy-rene of the formulae above and aninert carrier. Illustrative of such inert carriers are synthetic organicpolymeric substances, such as poly(vinyl chloride) resins.

A further embodiment of this invention is, in essence, a method forimparting photochromic properties to a substrate which comprisesincorporating in said substrate an elfective amount of a dihydropyreneas defined above. Illustrative of said substrates is poly(vinylchloride).

The 15,16-disubstituted-15,16-dihydropyrenes of this invention can beprepared in a variety of ways. One especially convenient syntheticpathway is outlined as follows:

R1 orrmsot R1 NaOH wherein R and R are as above defined. This sequence,

which will be fully exemplified in detail, generally combr 0 prisestreating a readily available or easily prepared trisubstituted phenolwith a methylating agent, such as dimethyl sulfate, followed byintroduction of chloromethyl groups into the remaining unsubstitutedpositions. (Of course, if it is desired that the ultimate productcontain substituents other than hydrogen at the 4, 5, 9 or 10 positions,it is convenient to introduce them at this step by using, for example,aldehydes other than formaldehyde, such as butyraldehyde orbenzaldehyde.) Next, the chlotime in the 3 and s-positions is replacedwith iodine by a reaction in which the chloroalkyl compound is treatedwith an iodide, such as sodium iodide. This provides a diiodo compoundwhich is treated then with a coupling reagent such as sodium andtetraphenylethylene until the formation of a cyclized derivative issubstantially complete. Next, the methoxyl groups are oxidized toquinone functional groups with ferric chloride, and the tri-cyclic ringsystem is converted to the tetra-cyclic ring system. Further oxidationis carried out with oxygen and base. The keto groups are reduced tomethylene groups with lithium aluminum hydride and aluminum chloride andthe desired 15.16 disubstituted 15,16 dihydropyrene is obtained bydehydrogenation over a palladium catalyst.

ttd m The 15,16-bridged compounds of this invention represented by theformula wherein R and R are as above defined can be prepared by a numberof techniques. Especially convenient is the synthetic pathway outlinedas follows:

R R 11+ Meso. +HCHO on,

I NaOH HQ}! on OMe ClCH

CHsCl OMB BUR

HCHO/HCI I ZnOlz/LiCl (1) MeMgI (2) FeCla (.)Mo ()Me R R nflqz ClCHHCHOIHCI I iMeMgI H: OH, I ZnCIz/LiGl I ClCH R -R R R OMe 0M1;

OMe 0 I I R R R R F8013 O1 CH2 C 2 K NaOH R i R R R OMe (L 1 LiAlHt lAlCl; (2) Pd/C wherein R is as hereinabove defined and Me means methyl.Of course, as will be obvious, compounds of this invention bearing Rgroups defined hereinabove, in the 4, 5, 9 and 10 positions can beprepared by haloalkylating the dimethoxydiphenylmethane with anappropriate aldehyde instead of formaldehyde. The above sequence will beexemplified in detail later; it comprises treating a 2,6-disubstituted-phenol with formaldehyde and an acid to form a bis-phenolderivative, which is converted to a dimethoxy derivative with dimethylsulfate. One aromatic hydrogen atom in each ring is next replaced with ahaloalkyl group, and methyl magnesium iodide and ferric chloride areused to form the tricyclic ring system. This compound isbis(chloromethylated) and the tetracyclic ring system is formed in thepresence of methyl magnesium iodide. This is converted to its quinonederivative with ferric chloride, then oxidized, reduced anddehydrogenated in a manner completely analogous to that used to preparethe corresponding 15,16-disubstituted 15,16- dihydropyrene describedabove.

The preparation of compounds wherein R is m being from 2 to 18, isaccomplished by forming a his phenolic compound in which the phenolradicals are joined para to para through a methylene bridge ofappropriate length, then using this as a starting material in thesequence outlined above. The corresponding o-arylene compounds areobtained if the bis phenolic starting material is joined para to parathrough adjacent carbon atoms in an aromatic ring.

The following examples are given solely for the purpose of illustrationand are not to be construed as limitations of this invention, manyvariations of which are possible without departing from the spirit orscope thereof.

Example I.1,3,6,8,l5,16-hexamethyl-l5,16- dihydropyrene (a)Methoxymesitylene.-2,4,6 trimethylphenol, 29.5 g., 0.217 mol, preparedby the procedure of Hart and Buehler, J. Org. Chem., 29, 2397 (1964),sodium hydroxide, 12.6 g., 0.316 mol, dissolved in 126 ml. of water, and19.7 ml. of dimethyl sulfate, 0.217 mol, are mixed in a vessel cooled inan ice bath. The temperature is raised and maintained at 50:1 C. for onehour, then 7.50 g. of sodium hydroxide in an equal weight of water and10 ml. (0.100 mol) of dimethyl sulfate are added at 3 hour intervalsduring 15 hours. The product is isolated by extraction of the aqueousreaction mixture with seven -ml. portions of ether. After washing theether layer with 25% sodium hydroxide and evaporating the ether, theresidue is fractionally distilled and 26.9 g. of methoxymesitylene, B.P.29 C./0.4-0.45 mm, 83% yield, is obtained.

(b) bis(chloromethyl)methoxymesitylene. A mixture of methoxymesitylene,7.4 g., 0.049 mol, paraformaldehyde, 7.82 g., 0.197 mol, lithiumchloride, 9.82 g., 0.245 mol, and zinc chloride, 4.80 g., 0.049 mol, isheated to C. and anhydrous hydrogen chloride is passed in. Addition ofgas is continued for 5 /2 hours at 72i2 C. during which timemonochloromethylated product, which appears first, is converted to thedesired bis chloromethylated product. The reaction mixture then ispoured into ml. of ice, and the solid material is collected on a filterand washed with water. There are obtained 11.5 g. ofbis(chloromethyl)methoxy mesitylene, 94% of theory. Recrystallizationfrom ethyl acetate yields 9.05 g., M.P. -136 C.

(c) Bis(iodomethyl)methoxymesitylene.Bis(chloromethyl)methoxymesitylene, 8.0 g., 0.0324 mol, sodium iodide,40 g., 0.26 mol, and 400 m1. of tetrahydrofuran are refluxed for 6hours. The reaction solvent is removed by distillation at 15 mm.pressure. Methylenechloride, 100 ml., and 300 ml. of ice water areadded. The aqueous phase, after separation of methylene chloride isextracted 4 times with 20 ml. of methylene chloride. The combinedorganic layers are percolated through 200 ml. of crushed calcium sulfatethen treated with decolorizing charcoal. The methylene chloride filtrateis concentrated in a vacuum to 30 ml. volume and 55 ml. of methanol are7 added. The precipitate is collected and recrystallized first fromtoluene, and then from ethyl acetate to yield 9.62 g. ofbis(iodomethyl)methoxymesitylene, M.P. l34138 C., 69% yield.

(d) 6,8,14,16,4,12 hexamethyl-7,l dimethoxy(2,2)- metacyclophane.Bis(iodomethyl)methoxymesitylene, g. in 50 ml. of dry tetrahydrofuran(THF) is added at 1 drop per second to sodium sand, g., 0.87 mol,suspended in 1 liter of refluxing THF and 2 g. of tetraphenylethylene.The system is stirred under nitrogen with a Vibromixed stirrer.Unreacted sodium is filtered off and the THF is removed by distillationin such a way that the pot temperature remains at or below C. Theresidual solid is dissolved in 250 ml. of methylene chloride. Thesolution is percolated through 15 g. of Florisil, then the methylenechloride is evaporated off leaving a residue, which is dissolved in ml.of hot carbon tetrachloride. The solid which precipitates on cooling iscollected and treated with 30 ml. of hot cyclohexane. The cyclohexanesolution is cooled and the desired product precipitates. There areobtained 11.7 g. of crude material which are chromatographed on alkalinealumina. After rcchromatographing, there is obtained 0.73 g. ofmaterial, M.P. 220-213 C.

(e) Bis dienone.The product of Step (d) is treated with ferric chloride.A solution of 1.00 g. of the methacyclophane in 100 ml. of drychloroform is stirred at room temperature for three hours with 3.5 g.ferric chloride. A precipitate of a reddish-brown inorganic complex ofthe bisdienone is formed and this is collected by filtration. This solidis immediately suspended in 100 ml. chloroform and 20 ml. 3 Nhydrochloric acid. This suspension is shaken until solution occurs; thechloroform layer is separated, washed with water and concentrated. Thereddish brown solid, about 1.2 g., is treated with charcoal in boilingethanol, filtered, and the ethanolic solution is concentrated to about20 ml. From the cold solution separates 0.9-1.0 g. of a yellow solid.

(f) Quinone.The prod-uct of Step (e) is treated with oxygen in thepresence of sodium hydroxide. A suspension of the bisdienone (190 mg.)in a solution of methanol ml.), water (15 ml.), and sodium hydroxide(2.5 g.) is stirred for 12 hours at room temperature. The resultingsolution is concentrated under reduced pressure, diluted with water (50ml.), and extracted with 20 ml. methylene chloride. The blue aqueouslayer is extracted again with solvent, and the combined organic extractsare dried and concentrated. The residue is sublimed at ISO-200 (0.1mm.). The orange sublimate is dissolved in chloroform, diluted withpetroleum ether, and after standing overnight at l0 the resultingcrystalline product (175 mg., 90%) is collected.

(g) Hexaene-The product of Step (1) is treated with lithium aluminumhydride and aluminum chloride. To a solution of 7 g. of aluminumchloride in 120 ml. of ether, 2 g. of powdered lithium aluminum hydrideis added with stirring, and the suspension is boiled under reflux for 2hours. After cooling, a 90 ml. portion of the clear supernatant iswithdrawn, transferred to a reaction flask and cooled to 80.

The quinone of Step (f) (300 mg.) in 10 ml. benzene is added to 200 ml.of ether and the suspension added dropwise with stirring to the mixedreducing agent at -80 C. over a 2 hour period. The suspension is slowlywarmed to room temperature and boiled for 0.5 hour. After destroying theexcess reagent with ethyl acetate followed by water, and separation ofthe ether layer, evaporation under reduced pressure yields a greenresidue which is unstable to light and air.

(h) Dihydropyrene.-The product of Step (g) is treated with palladium anddehydrogenated. A suspension of 50 mg. of 5% palladium-charcoal in 25ml. of benzene containing 1 ml. of acetone is refluxed for 15 minutes.To this mixture is added 50 mg. of the above green solid and hcatnig iscontinued for 6 hours. The suspension is cooled,

G. Geon l03-EP resin 100.0 Advastate T3 stabilizer 2.0 Stearic acid 0.5

l,3,6,8,15,16-hexamethyl-l5,16-dihydropy1'ene 0.005

The dihydropyrene is solvent blended (methylene chloride) with thepowdered poly-vinyl chloride) and other additives and the solvent isevaporated. The batch is milled on a two-roll plastics mill for 5minutes at 350 C. The milled sheet is compression molded at 365 F. intofour 5 x 5 x 0.045 inch sheets in a picture frame mold. (Molding cycle:5 min. at contact pressure; 45 sec. at 5 tons, 45 sec. at 10 tons, 45sec. at 15 tons, 45 sec. at 20 tons, then flash quench in cold water.)The colored plastic films clear on exposure to light and returns to acolored form when left in the dark.

Example lI.-15,16-methylene-1,3,6,8-tetramethyl- 15,16-dihydropyrene (a)4.4'-methylene bis(2,6-xylenol).-The reaction of 2,6-xylenol (122 g.,1.0 mol in 120 ml. of absolute ethan01), trioxane (18 g., 0.6formaldehyde eq. in 170 ml. absolute ethanol) conc. hydrochloric acid(120 ml., 1.32 mols) atfords the bis-xylenol in good yield. The trioxanesolution is added over 2.75 hours to a reaction mixture kept undernitrogen at 50-* 1 C. The white product is collected after the reactionmixture has been cooled to -60 C. Washing of the reaction product with aminimum of cold absolute ethanol and drying of the washed product.aifords 101.1 g., yield, M.P. 172.5-177 C. Recrystallization from a30:70 mixture of ethyl acetate-heptane provides 92.0 g., 72% yield, oflong needles, M.P. 175- 178 C.

(b) 4,4'-methylene bis(2,6-dimethylanisole).-Dimethyl sulfate 89 g.,0.705 eq.) is added dropwise during 1 hour to 4,4-methylene bis(2,6-xylenol) (90.0 g., 0.705 eq., M.P. 175-178) which has beendissolved in aq. sodium hydroxide (42.4 g., 1.06 mols, in 425 ml. ofwater). Thereafter, smaller quantities of sodium hydroxide (21.2 g.,0.53 mol) in one portion and dimethyl sulfate (46 g., 0.35 mol) areadded dropwise to the reaction mixture (50i5 C.) at hourly intervals.This treatment is repeated for seven hours. The reaction is completed byadding more sodium hydroxide (21.2 g., 0.53 mol), by slowly dropping ina final charge of dimethyl sulfate (89 g., 0.705 eq.) and by refluxingfor an additional 1.5 hours. After cooling to room temperature the solidis collected and dissolved in a mixture of ethyl ether (400 m1.) andwater (400 ml.). The ether extract is washed with 25% sodium hydroxide(2X 25 ml.) and with saturated sodium chloride (2x 25 ml.), then driedovernight. Removal of solvent by distillation aflords 75 g., 75% yield,136-145 "l 0.10 mm., M.P. 78-82.

(0) 4,4 methylene bis(3-chloromethyl-Z,6-dimethylanisole).-Hydrogenchloride is bubbled into a stirred mixture of trioxane (16.9 g., 0.564mol), lithium chloride (19.2 g., 0.141 mol) and glacial acetic acidml.). After ten minutes (exotherm 25 to 38 C.) the reaction mixturebecomes clear and homogenous. 4,4'-methylenebis(2,6-dimethylanisole) isthen added in one portion (10.0 g., 0.0347 mol). The reaction proceedsrapidly /z hour) on a steam bath (pot 80-87 C.). The white product isisolated by mixing the reaction slurry with ice (200 ml.), by washingthe filtered solid (M.P. 131-133 C.), which has been dissolved inchloroform, with 10% sodium bicarbonate solution until neutral and byevaporating off the dried solvent. Recrystallization from ethyl acetate(14) affords 19.7 g., 73% yield, M.P. 135-137 C. NMR shows the presenceof only one sharp methoxy 9 singlet (3.69 6, p.p.m.) indicatingchloromethyl groups at the 3,3 positions.

(d) 4,4 methylene 3,3 (1,2-ethylene) bis(2,6- dimethylanisole.Compoundof Step (c) (19.0 g., 0.105 eq. in 1 l. absolute ether) is condensed tothe abovenamed product on addition to methyl magnesium iodide (methyliodide 14.9 g., 0.105 mol; magnesium, 2.50 g., 0.103 mol; 300 ml. abs.ether). The bis chloromethyl compound is added under prepurifiednitrogen over a period of 18 hours. The condensed product is obtained bychromatography on alumina. Elution with pet. ether affords 6.3 g., 55%yield, of white powder.

(e) 4,4 methylene 3,3 (1,2 ethylene) bis[5,5'- bis (chloromethyl-2,6-dimethylanisole] .Anhydrous hydrogen chloride is bubbled into amixture of trioxane (2.4 g.) zinc chloride (2.7 g), lithium chloride(1.7 g.) and glacial acetic acid ml.) to give a homogeneous solution tobis-chloromethyl ether. The double bridged compound is added in oneportion (3.1 g.) and the temperature kept at 50:1" C. for 8 hours. Theproduct is isolated by pouring the reaction mixture into ice ml.) andextracting with methylene chloride. The extracts, washed with 2X 10 ml.of 10% sodium bicarbonate, 2X 5 ml. saturated sodium chloride solution,are dried overnight. Recrystallization from toluene affords 3.0 g., 74%yield, of white plates.

(f) 4,12-methylene metacyclophane.The compound of Step (e) (1.0 g.)reacts with zinc dust (0.177 g.), sodium carbonate (0.260 g.) and acatalytic amount of sodium iodide to give the 4,12-methylenemetacyclophane. The hot reaction mixture is poured into ice (100 g.) andis extracted with methylene chloride. The extract is washed with water.After the solvent is stripped off, steam distillation provides about an80% yield of white needles.

g) Bis dienone-The metacyclophane of Step (f) (0.66 g.) and anhydrousferric chloride (2.0 g., 1.2 mol) dissolved in anhydrous chloroform (80ml.) are stirred at room temperature for 6 hours to give an insolublereddish brown complex. The complex is collected by filtration and isdecomposed by vigorously shaking with a mixture of chloroform (70 ml.),dilute hydrochloric acid (3 N, 15 ml.) until solution is complete. Theseparate chloroform layer is concentrated and the red-brown solid isdissolved in 70 ml. of hot ethanol. The hot solution is treated withcharcoal and is concentrated to 15 ml. On cooling yellow needles aredeposited in about 90% yield.

(h) Quinone.A suspension of the compound of Step (g) (0.50 g., 163 mol)and a water-methanol (70 ml., 150 ml.) solution of sodium hydroxide (10g., 0.25 mol.) are stirred for 18 hours at room temperature. Theresulting solution is concentrated under a water pump, diluted withwater (200 ml.) and extracted with methylene chloride (90 ml.). Theaqueous layer is extracted further with 225 ml. portions of solvent andall extracts were combined, washed with water, evaporated under a waterpump and sublimed (100 C./0.01 mm.) to give a violet solid.Recrystallization from chloroformcyclohexane affords orange needles inabout 90% yield.

(i) 15,16 methylene 1,3,6,8 tetramethyl 15,16 dihydropyrene.A reducingsolution is prepared by adding lithium aluminum hydride (2.0 g.) to anether (120 ml.) solution of aluminum chloride (7.0 g.) stirring andrefiuxing the mixture for 2 hours and then transferring 80 ml. of cooledsupernatant liquid to a preassembled and dried reaction set-up. Dropwiseaddition of quinone of Step (h) (0.340 g. dissolved in 10 ml. benzeneand diluted to 200 ml. with dry ether) to the reducing solutionmentioned above at 80 over 2 hours, time yields a mixture of the desiredproduct and a dihydro product. The suspension is warmed to roomtemperature (1 hour) and then refluxed for /2 hour. The excess reducingagent is decomposed with ethyl acetate and enough water ml.) is added togive two phases. The separated ether phase is dried under vacuum. Theresulting blue solid is then refluxed in cyclohexane (200 ml.) withpalladium on r 10 charcoal (0.300 g.) for 18 hours to completedehydrogenation of the dihydro product. After filtration and removal ofthe reaction solvent the blue solid is sublimed 0.02 mm.) to yield theproduct in about 60% yield. The following list sets forth some of thecompounds Within the scope of this invention prepared by the proceduresof the foregoing examples and disclosure. The list is given to avoidunnecessary repetition of experimental details:

15, 16-(1,18-octadecylene)-1,3,6,8-tetramethyl-15,16-

dihydropyrene 15, 16-( 1,2-phenylene) -1,3,6,8-tetramethyl-15,16-

dihydropyrene 15, 16-methylene-15,l 6-dihydropyrene1,3,4,5,6,8,9,10,15,16-decamethyl-15,16-dihydropyrene1,3,6,8-tetracyclopropyl-15,16-dimethyl-15, 16-dihydropyrene1,3,6,8-tetraphenyl-15,16-dimethyl-15,16-dihydropyrene4,5,9,10-tetraphenyl-15,l6-dimethyl-15,16-dihydropyrene 1,3,6,8-tetra(chloromethyl) -15-l6-dimethyl-15,16-dihydropyrene1,3,6,8-tetra(bromomethyl) -15,16-methylene-15,l6-dihydropyrene1,3,6,8-tetra(cyanomethyl)-15,16-dimethyl-15,l6-dihydropyrene 1,3,6,8-tetra(carbamylmethyl) -15,16-dimethyl-l5,16-

dihydropyrene 1,3,6,8-tetra(carboxymethyl)-15,16-dimethyl-l5,16-dihydropyrene 1,3,6,8-tetra(carboethoxymethyl) -15,16-dimethyl-15,16-

dihydropyrene 1,3 ,6,8-tetramethyl-15,16-( 1',2-dimethylethylene)-15,16-

dihydropyrene 1,3 ,6,8-tetramethyl-15,16-diphenyl-15,16-dihydropyrene1,3 ,6,8-tetramethyl-15,16-di(chloromethyl)-15,16-dihydropyrene1,3,6,8-tetramethyl-15,16-di(cyanomethyl)-15,16-dihydropyrene 1,3,6,8-tetramethyl-15,16-di(carboxymethyl)-15,16-

dihydropyrene lower alkyl lower alkyl on. CH3

| I lower alkyl L/ lower alkyl 4. A compound of the formula:

wherein R is hydrogen or lower alkyl.

5. 15,16-methylene-15,16-dihydropyrene.

(References on following page) 11 12 References Cited W. 5. Lindsay etal.: J. Amer. Chem. Soc., 83, pp. UNITED STATES PATENTS 1 2508295 5/1950Rechmeyer H. R. Blattman et aL: J. Amer. Chem. Soc., 87-(1), 3,231,58411/1960 Berman et a1. :52 300 1304. 1965- 3,278,449 11/1966 Hardwich eta1. 252300 a V. Boekelheide et aI.: J. Amer. Chem. Soc., 85, 1545- OTHERREFERENCES 1963' 5 ct Bull Chem" Belgian IDELBERT E. GANTZ, PrimaryExaminer.

Monique De Clercq et al.: Bull. Soc. Chem, Belgian 110 V, OKEEFE,Assistant Examiner. 64, pp. 367-385, 1955.

